Being afraid of new experiences may
lead to a shorter life, new research in rats suggests.

Rats that were more fearful produced
more stress-related hormones when exposed to new experiences and
they tended to live shorter lives than less adventurous rats,
researchers report.

"Young rats identified as fearful
produce more stress hormones across the life span," Dr. Sonia
Cavigelli of the University of Chicago's Institute for Mind and
Biology told Reuters Health. The increased production of stress
hormones may accelerate aging, she said.

Whether the same is true in people
is uncertain, but studies have shown that shy children experience
a surge in stress hormones when confronted with something new.

"We should consider how personality
and other behavioral traits affect our physiology and what kind
of impacts these traits could have on our health over the life
span," Cavigelli said.

In rats that were more fearful
than others, the trait showed up early in life and persisted throughout
life, Cavigelli and Dr. M. K. McClintock report in the early online
edition of the journal Proceedings of the National Academy of
Sciences.

When placed in a new environment,
fearful rats were hesitant and did not explore their new surroundings
very much. In contrast, rats that were not fearful moved throughout
their new surroundings and inspected objects around them.

Fearfulness was apparent in rats
early in life, even before they were weaned, and it persisted
into adulthood, according to the report. Compared to other rats,
fearful rats experienced a surge in hormones called glucocorticoids
after being exposed to something new.

What's more, fearful rats lived
an average of 20 percent shorter lives than more adventurous rats.

The association between increased
secretion of stress hormones and a shorter life suggests that
the hormones may gradually cause damage that accelerates aging,
according to the researchers.

But it is important to note, according
to Cavigelli, that fearfulness or shyness may not always be a
negative trait.

"I believe that this fearful trait
may actually be quite beneficial, for example," Cavigelli said.
"It may be the one thing that keeps individuals from engaging
in needless risky behavior."

Future research should focus on
how social experiences early in life affect the development of
fearfulness, according to the Chicago researcher. For example,
one question that needs to be answered is how early social interactions
affect the development of fearfulness, she said.

In addition, future studies in
rats may identify other health-related differences between fearful
and adventurous rats, Cavigelli said.